diff --git a/.changeset/polite-wombats-smash.md b/.changeset/polite-wombats-smash.md
new file mode 100644
index 0000000000..250ca215f5
--- /dev/null
+++ b/.changeset/polite-wombats-smash.md
@@ -0,0 +1,6 @@
+---
+'@backstage/backend-app-api': patch
+'@backstage/errors': patch
+---
+
+Add NotImplementedError
diff --git a/packages/backend-app-api/src/http/MiddlewareFactory.ts b/packages/backend-app-api/src/http/MiddlewareFactory.ts
index dc9fe9aa5f..833bdba540 100644
--- a/packages/backend-app-api/src/http/MiddlewareFactory.ts
+++ b/packages/backend-app-api/src/http/MiddlewareFactory.ts
@@ -38,6 +38,7 @@ import {
   NotModifiedError,
   serializeError,
 } from '@backstage/errors';
+import { NotImplementedError } from '@backstage/errors';
 
 /**
  * Options used to create a {@link MiddlewareFactory}.
@@ -257,6 +258,8 @@ function getStatusCode(error: Error): number {
       return 404;
     case ConflictError.name:
       return 409;
+    case NotImplementedError.name:
+      return 501;
     default:
       break;
   }
diff --git a/packages/errors/src/errors/common.ts b/packages/errors/src/errors/common.ts
index 80a3d84d82..e1a292d7b5 100644
--- a/packages/errors/src/errors/common.ts
+++ b/packages/errors/src/errors/common.ts
@@ -74,6 +74,13 @@ export class ConflictError extends CustomErrorBase {}
  */
 export class NotModifiedError extends CustomErrorBase {}
 
+/**
+ * The server does not support the functionality required to fulfill the request.
+ *
+ * @public
+ */
+export class NotImplementedError extends CustomErrorBase {}
+
 /**
  * An error that forwards an underlying cause with additional context in the message.
  *
diff --git a/packages/errors/src/errors/index.ts b/packages/errors/src/errors/index.ts
index 9e1c2408af..efd3257fbf 100644
--- a/packages/errors/src/errors/index.ts
+++ b/packages/errors/src/errors/index.ts
@@ -24,6 +24,7 @@ export {
   NotAllowedError,
   NotFoundError,
   NotModifiedError,
+  NotImplementedError,
 } from './common';
 export { CustomErrorBase } from './CustomErrorBase';
 export { ResponseError } from './ResponseError';